Network Working Group C. Daboo
Request for Comments: 5235 January 2008
Obsoletes: 3685
Category: Standards Track
Sieve Email Filtering: Spamtest and Virustest Extensions
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Sieve email filtering language "spamtest", "spamtestplus", and
"virustest" extensions permit users to use simple, portable commands
for spam and virus tests on email messages. Each extension provides
a new test using matches against numeric "scores". It is the
responsibility of the underlying Sieve implementation to do the
actual checks that result in proper input to the tests.
Table of Contents
1. Introduction and Overview .......................................2
2. Conventions Used in This Document ...............................2
3. Sieve Extensions ................................................3
3.1. General Considerations .....................................3
3.2. Test spamtest ..............................................3
3.2.1. spamtest without :percent Argument ..................4
3.2.2. spamtest with :percent Argument .....................5
3.3. Test virustest .............................................7
4. Security Considerations .........................................9
5. IANA Considerations .............................................9
5.1. spamtest Registration ......................................9
5.2. virustest Registration ....................................10
5.3. spamtestplus Registration .................................10
6. References .....................................................10
6.1. Normative References ......................................10
6.2. Informative References ....................................11
Appendix A. Acknowledgments .......................................12
Appendix B. Important Changes since RFC 3685 ......................12
Daboo Standards Track [Page 1]RFC 5235 Sieve: Spamtest and Virustest Extensions January 20081. Introduction and Overview
Sieve scripts are frequently being used to do spam and virus
filtering either based on implicit script tests (e.g., tests for
"black-listed" senders directly encoded in the Sieve script), or via
testing messages modified by some external spam or virus checker that
handled the message prior to Sieve. The use of third-party spam and
virus checker tools poses a problem since each tool has its own way
of indicating the result of its checks. These usually take the form
of a header added to the message, the content of which indicates the
status using some syntax defined by the particular tool. Each user
has to then create their own Sieve scripts to match the contents of
these headers to do filtering. This requires the script to stay in
synchronization with the third-party tool as it gets updated or
perhaps replaced with another. Thus, scripts become tied to specific
environments and lose portability.
The purpose of this document is to introduce two Sieve tests that can
be used to implement "generic" tests for spam and viruses in messages
processed via Sieve scripts. The spam and virus checks themselves
are handled by the underlying Sieve implementation in whatever manner
is appropriate, so that the Sieve spam and virus test commands can be
used in a portable way.
In order to do numeric comparisons against the returned strings,
server implementations MUST also support the Sieve relational
[RFC5231] extension, in addition to the extensions described here.
All examples below assume the relational extension is present.
2. Conventions Used in This Document
Conventions for notations are as in [RFC5228] Section 1.1.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The term "spam" is used in this document to refer to unsolicited or
unwanted email messages. This document does not attempt to define
what exactly constitutes spam, or how it should be identified, or